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While you can collapse fasttabs on pages, you cannot collapse the listpart on those pages unless they have been designed in a group by the developer.

As an example, it is not possible to collapse the sales lines on a sales invoice.
Category: General
STATUS DETAILS
Completed
Ideas Administrator

Good news! We released this feature as part of the functionality in Collapse and expand document lines, but it works for most pages having parts in the content area of the page.

Please refer to the following link for more information:
https://docs.microsoft.com/en-us/dynamics365-release-plan/2020wave1/dynamics365-business-central/collapse-expand-document-lines

Best regards,
Mike Borg Cardona
Program Manager, Microsoft